Polyolefins such as polyethylene and polypropylene are the most important plastic materials as industrial materials and are widely commonly used in packaging materials and electrical materials as extrusion-molded articles and the like, in industrial materials such as automobile parts and home appliances as injection-molded articles, and further, in a variety of applications such as fiber materials and building materials.
As such, since the use applications are extremely wide and are diversified, in polyolefins, from the viewpoints of their applications, the improvement and enhancement in various properties have been continuously sought and, in order to meet such demands, technical development has been achieved mainly by improving polymerization catalysts.
The catalytic activity has been enhanced by a Ziegler catalyst utilizing a transition metal compound and an organometallic compound, and thus industrial production has been realized. Thereafter, there have been made various improvements in performance, such as an improvement in polymer physical properties by controlling molecular weight distribution and an improvement in stable productivity in plants by controlling particle properties.
Specifically, there has been developed a catalyst using a solid catalyst component containing a magnesium compound as a catalyst support and titanium and halogen as essential components. Further, there have been proposed a catalyst showing enhanced catalytic activity and stereoregularity using an electron-donating compound (e.g., see Patent Document 1) and thereafter, a catalyst showing further enhanced catalytic activity and stereoregularity using a specific organosilicon compound (e.g., see Patent Documents 2 and 3).
Moreover, by using a silicon compound of a special structure having an alkenyl group such as a vinyl group or an allyl group in combination, in addition to the specific organosilicon compound, there has been proposed a catalyst having such performance improvements that not only the catalytic activity and stereoregularity are further improved but also response of hydrogen to be used as a molecular weight modifier is made satisfactory (e.g., see Patent Documents 4 to 6).
Furthermore, there has been also proposed a technique of catalyst increasing bulk density of the resulting polymer, improving particle properties, and enhancing productivity of the polymer by using a specific dialkoxymagnesium as a magnesium source (e.g., see Patent Document 7).